This invention relates to a transversal engine four-wheel drive vehicle.
Generally, there is created rotational speed difference accompanied by difference in a turning radius between front wheels and rear wheels in turning of a four-wheel vehicle. When a four-wheel drive vehicle is turned on a road surface having a high coefficient of friction such as a paved road where slippage between the road surface and drive wheels is seldom created, there is disadvantageously generated a return torque (rotational difference of the drive shafts) between the front wheel drive shaft and the rear wheel drive shaft. For this reason, it is generally prevented that drivability is impaired, that wear of a tire is increased, and that durability is deteriorated. The four-wheel drive vehicle is classified into a part-time type adapted to switch from four-wheel drive to two-wheel drive on the road surface having a high coefficient of friction such as the paved road and a full-time type (normally four-wheel drive conditioned) having a center differential mechanism for dividedly transmitting power to the front wheel drive shaft and the rear wheel drive shaft.
The conventional full-time four-wheel drive vehicle having a transversal engine is provided with a front wheel differential gear for dividedly transmitting the power to a front right wheel and a front left wheel, a rear wheel differential gear for dividedly transmitting the power to a rear right wheel and a rear left wheel, and the center differential mechanism. Therefore, if only one of the drive wheels is separated from the road surface or slips, that is, negative load is removed, the divided power is not disadvantageously transmitted to the other three drive wheels. To solve the problem, the center differential mechanism of the conventional full-time four-wheel drive vehicle includes a differential locking mechanism for locking a differential mechanism of the center differential mechanism by a mechanical operating means (which is designed to generate differential resistance in a friction mechanism with the aid of a cam mechanism or a spring force) to be operated by increased output difference of torque transmitted to the front wheel drive shaft and the rear wheel drive shaft, and limiting the torque to be transmitted to the front wheel drive shaft and the rear wheel drive shaft, whereby the power may be transmitted to the other three wheels even if only one of the drive wheels is separated from the road surface.
However, in the conventional full-time four-wheel drive vehicle having a transversal engine, as the differential locking mechanism for locking the differential mechanism of the center differential is mechanically operable by the increased output difference in the torque to be transmitted to the front wheel drive shaft and the rear wheel drive shaft, there are the following problems in the prior art:
(1) The differential gear cannot be arbitrarily locked.
(2) It is difficult to set an initial timing of differential locking in the mechanical differential locking mechanism.
(3) The initial timing of differential locking cannot be made variable according to a vehicle running condition.